Composition and structure of tin/vanadium oxide surfaces for chemical sensing applications

The aim of this study is to obtain data useful to elucidate the sensing mechanism of solid state microsensors for hydrocarbon detection based on mixed vanadium/tin oxides. The sensors studied here were prepared by deposition of an active layer of Sn and V oxides on pre-oxidized porous silicon. The surface composition of these sensors was studied by a combination of low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). Parallel studies were performed on a ‘model’ system prepared by depositing a thin film of vanadium on a single crystal SnO2(1 1 0) surface and by successive thermal treatment. The results obtained show that vanadium is detectable by LEIS in the topmost atomic layer of both the polycrystalline and the s.c. sample in similar amounts. On the model system, the results of X-ray photoelectron diffraction (XPD) measurements show the formation of epitaxial VO2. The main conclusions of the present study are that in these sensors vanadium and tin oxide form separate phases and that vanadium species are present in the outermost surface. Both phases may take an active part in the mechanism of hydrocarbon detection in these sensors.